GENERAL BACKGROUND ART
Keyboards are essential input devices for many applications, including for personal computers. As described above, such personal computers are often designed to be transportable and have been occupying less cubic volume over time. An example of such a portable personal computer is described in coassigned U.S. Pat. No. 5,198,991, incorporated by reference herein for the purpose of describing the computer per se and the connections between the computer and a folding keyboard, and such description will not be repeated here.
The miniaturization of data processing equipment, for portability and ease of use, is becoming increasingly important. However, there are some factors which place practical limits on the miniaturization which could theoretically be achieved.
The limiting factor for reducing the size of portable data processing equipment is generally the keyboard. A keyboard requires sufficient size, in terms of horizontal dimensions, for the keys. Keys are constrained to at least a certain minimum size, because they must have a size and spacing commensurate with the size of an average operator's fingers and hands.
Keyboards also requires mechanics, for converting keystrokes to electrical signals representative of operation of the keys. Some minimum thickness must be provided for these components. Also, the keys preferably have enough vertical displacement to give the user a good tactile feel.
Some conventional keyboards, particularly full-size desktop computer keyboards, have used mechanics such as "chimneys," sleeves that slide up and down. Such structures provide the advantage that all parts of the key are stable pressing down. That is, the key is constrained to a single, vertical translational degree of freedom, so the key presses down in a vertical fashion.
Another conventional structure that of using scissors that use two members that pivot at the center and are attached at one end and the other end of them slides a lot, one can achieve pressing anywhere on the key (pressing the key vertically up and down.
Prior U.S. Pat. No. 5,280,147, Mochizuki et al., assigned to Brother Kogyo Kabushiki Kaisha, reduces the thickness of the keyboard by the use of scissors-like pivotally connected support levers with pivot connections at one end of each lever to respectively the base and the key, and sliding pivot connections at the opposite ends. A conventional nonlinear rubber spring or "dome" is used to transmit the keystroke to electrical contacts to make the connection, indicating operation of the key.
These mechanisms are fine for desktop keyboards, when there is vertical space to be had. However, they are less suitable for portable computers. Such computers are designed for small size and light weight. In particular, reducing the thickness, and producing a "thin" keyboard, has been an important design objective. For such thin keyboards where there is little vertical space, other mechanisms have been used.
A typical portable data processor, or "portable personal computer" or "personal digital assistant", has a keyboard panel and a display panel, and the data processor is incorporated within one of the panels. The two panels are then folded together so that the bottom of the keyboard panel and the back of the display panel form an outer case for the folded unit. By reducing the thickness of the keyboard, the thickness of the overall folded unit may also be reduced, making the folded portable data processing unit easier to handle and to carry.
Prior U.S. Pat. No. 5,457,453, Chiu et al., unassigned, illustrates a keyboard having reduced thickness when folded, by moving otherwise conventional plunger keys to depressed positions when folding is to occur.